There is a growing desire to use point to multi-point services in wireless communication systems. As shown in FIG. 1 in point to multi-point, one service is sent from a single point, such as a base station, to multiple points, such as user equipments. Examples of point to multi-point services are multimedia broadcasts and multicast services.
In the third generation partnership program (3GPP) proposed system, one proposed channel that could be used for such services is the forward access channel (FACH). The FACH is a downlink common transport channel (TrCH) that can be received by all users. The FACH TrCH is broadcast by applying it to the secondary common control physical channel (S-CCPCH). The S-CCPCH is transmitted to all the cell users.
To limit the radio resources allocated to the S-CCPCH, the S-CCPCH data rate is limited. To illustrate, if a high data rate service was transmitted over the S-CCPCH, it would need to be transmitted using a low data redundancy to achieve that high data rate. Since the S-CCPCH is transmitted to the entire cell, it is transmitted at a power level sufficient for reception by a user at the periphery of the cell at a desired quality of service (QOS). Broadcasting a high data rate service at this power level would increase interference to other users reducing the capacity of system, which is extremely undesirable.
Due to the broadcast nature of the S-CCPCH and FACH, the radio resources required for the S-CCPCH and FACH are rather static. The modulation and coding set (MCS) and transmission power level used by the S-CCPCH needs to be sufficient to maintain a desired QOS at the periphery of the cell.
A shared channel proposed for use in the 3GPP system is the high speed downlink shared channel (HS-DSCH). The HS-DSCHs are high speed channels which are time shared by the cell users (user equipments). Each transmission is targeted to a separate user and each user's transmission over the HS-DSCH is separated by time.
The HS-DSCH transmissions to a user are associated with an uplink and a downlink dedicated control channels. Each user sends measurements via layer 1 and layer 3 signaling in the uplink control channel. Using these measurements, a modulation and coding set (MCS) is selected for that user's transmissions. The MCS can be changed every 2 to 10 milliseconds. By carefully selecting the MCS for the user transmissions, the least robust (lowest data redundancy) MCS can be selected to maintain the desired quality of service (QOS). As a result, the radio resources are more efficiently utilized.
To determine when a particular user's transmission is being sent over the HS-DSCH, that user first searches on the set of downlink control channel for its UE ID encoded in a cyclic redundancy code (CRC) and decodes the downlink control channel for HS-DSCH allocation information. After a predetermined period, the UE receives the HS-DSCH for a packet having its UE ID and decodes that packet for reception of user data.
Although the HS-DSCH allows for a more efficient utilization of radio resources, only point to point services can be handled by the HS-DSCH. To handle multiple reception points, multiple transmissions must be made over the HS-DSCH. Such multiple transmissions utilize a large amount of radio resources, which is undesirable.
Accordingly, it is desirable to have a flexible mechanism to provide point to multi-point services.